1. Field of the Invention
The present invention relates to a method for stabilizing the optical output of a semiconductor laser (laser diode).
2. Description of the Related Art
Conventionally, semiconductor lasers are used in various fields. Since the semiconductor lasers are more responsive than gas lasers and the like, for example, the semiconductor lasers are often used as light sources in image exposure apparatuses and the like. In such cases, sometimes the semiconductor lasers are intermittently driven. For example, a semiconductor laser is driven for 15 seconds for image exposure, and stopped for 10 seconds for replacement of an exposed photosensitive material with a new photosensitive material.
When a semiconductor laser is driven as above, it is desired that the output power of the semiconductor laser reaches a predetermined level immediately after start of driving (for example, within one second), and thereafter the predetermined level is maintained.
In a conventionally known method for stabilizing the optical output of a semiconductor laser, variations of a laser-light output corresponding to a control signal for a laser light source is measured in advance, the variation pattern is recorded, and the control signal is corrected according to the variation pattern, as disclosed in, for example, Japanese Unexamined Patent Publication No. 11 (1999)-284284.
However, in the above method disclosed in Japanese Unexamined Patent Publication No. 11 (1999)-284284, it is very difficult to stabilize the optical output immediately after (within about one second of) startup of the semiconductor laser. Further, although GaN-based compound semiconductor lasers which oscillate in the blue wavelength range are known, it is particularly difficult to stabilize the optical outputs of this type of GaN-based compound semiconductor laser immediately after their startup.